1. Field of the Invention
This invention relates to fasteners and more specifically to blind fasteners or nuts, sometimes referred to as anchor bolts or toggle bolts when associated with bolts provided with threads or other types of cooperating fastening means.
2. Description of the Prior Art
Blind nut or anchor bolt assemblies are often used in the mounting of fixtures or structural elements on wall or panels in situations in which it is impossible or difficult to hold a nut on the back or "blind" side of the wall or panel. One class of blind bolt assembly is characterized in that the blind nuts used therein have threaded portions to which are connected retaining surfaces of unstressed configurations such that they may be pushed through an aperture in the wall or panel, the retaining surfaces being expanded by various means as a bolt or screw is threaded through the nut to engage and be tightened against the back of the wall or panel. In the prior art such devices have been made of unitary die stampings of metal or of molded plastic materials and are exemplified by U.S. Pat. Nos. Re. 22,543; 2,876,167; 2,762,252; 3,143,915; 3,174,387; 3,937,004; and 3,888,156. Such devices while in substantial use, are disadvantageous in that they require the inclusion of means to engage the outside of the wall or panel; that they sometimes are limited in use to a particular thickness of panel; and that they must either be of light gage material to permit the necessary deformation or require excessive force in installation.
A second type of blind nut is characterized in that it has a pair of spring biased or resilient outwardly extending wings which are attached to a threaded center portion, the wings being of a size to extend in normal unstressed condition a length greater than a dimension of the hole in the panel through which it is intended to make a connection. The wings are squeezed together as they are inserted through the prepared aperture in the panel and expand and engage the back side of the panel as a bolt or screw is threaded through the threaded center portion. The most used such device is a four piece blind nut assembly which is comprised of a threaded hinge piece which forms a pivotal connection for two wing members and a spring associated with the hinge piece and the wing members for biasing the wing members toward outwardly extending disposition. An example of a one-piece structure which seeks to duplicate the functioning of the multi-part blind nut is a unitary structure shown in U.S. Pat. No. 3,363,501 issued to H. J. Modrey on Jan. 16, 1968. The Modrey patent describes and claims a single-piece stamping of resilient metal and of a shape such that it may be formed into a threaded shank having two outwardly and upwardly extending spring fingers or wings which are adapted to be squeezed together for insertion into an opening in a panel to perform the blind nut function previously described.
There are certain disadvantages to the last described type of blind nut (deformable for insertion) as exemplified in the prior art. The multi-piece arrangement described above is subject to the disadvantages of complexity and relatively high material and labor costs involved in manufacture and assembly of the several parts. Moreover, although such devices are advantageous in that they can be used for connections to panels of varying thickness and in that they provide larger areas of contact with the inner side of the panel, they are disadvantageous in that the separate hinge piece which must be used requires an enlarged aperture in the panel to which a connection is desired to be made.
Efforts to simulate the structurally preferable multi-piece blind nut in a one-piece structure, as exemplified by the Modrey patent mentioned above, have been disadvantageous in that the metal versions have required further reshaping after the stamping of the necessary forms in order to provide an annulus for engagement with the threads of a bolt or screw. Such devices, as exemplified by the Modrey patent, are also disadvantageous in that they provide only small areas of contact with the back side of the panel which may damage the panel so that they must be used with panels of adequate minimum strength and thickness. Moreover, these small areas are at the ends of narrow arms which tend to be deformed beyond the elastic limit of the material of which they are made as the nut is tightened into position.